1. Field of the Invention
The present invention relates to surgical cutting instruments for cutting tissue, and more particularly to an instrument for use with an endoscope for cutting ligaments or muscles such as the ligaments in the hand during surgical procedures such as endoscopic carpal tunnel release.
2. Discussion of the Related Art
Endoscopic surgical cutting instruments for performing surgical procedures such as carpal tunnel release are well known in the art. These devices typically include a cutting blade which is extendible or pivotable from an end portion of the instrument and is used to decompress the carpal tunnel in the hand.
Carpal tunnel syndrome is a condition of the hand which typically results in loss of feeling, weakness or numbness (paresthesia) in the fingers and hand. In general, repetitive, short stroke motion of the fingers and hand may lead to irritation of the median nerve which passes through the carpal tunnel, and this irritation or inflammation may lead to pain, weakness of the muscles and general numbness in the fingers and hand. The carpal tunnel is an area in the hand adjacent the wrist which is bounded by the carpal bones of the hand and the transverse carpal ligament. The median nerve and flexor tendons pass through the tunnel to control movement of the fingers. As the median nerve becomes irritated, or as the transverse carpal ligament is thickened due to repetitive motions of the hand and wrist, compression of the nerve inside the carpal tunnel leads to carpal tunnel syndrome and its associated degenerative conditions.
In order to treat carpal tunnel syndrome, it has been known to cut or divide the transverse carpal ligament, also known as the flexor retinaculum, to provide for decompression of the carpal tunnel. Historically, the division of the transverse carpal ligament was done during open surgical procedures which involved slitting the palm of the hand to expose the ligament prior to cutting the ligament. Recently, instrumentation has been developed to allow this procedure to be performed endoscopically, with a small incision at the base of the wrist to allow for division of the ligament beneath the skin. Once the ligament is cut, it allows for additional space in the carpal tunnel area to relieve the irritation and pressure on the median nerve.
Several instruments are known for performing endoscopic decompression by division of the transverse carpal ligament. An instrument known as the Paine retinaculotome, as described in the Journal of Neurosurgery, Vol. 59, Dec. 1983, pp. 1031-1036, provides a cutting edge which is engagable with the transverse carpal ligament on the wrist side of the ligament. The Paine instrument is inserted into the hand through an incision at the base of the wrist. As the ligament is engaged by the cutting instrument, the instrument is advanced forward into the hand to divide the ligament. A similar instrument is disclosed in U.S. Pat. No. 5,029,573 to Chow which provides a cannula that is inserted into the hand at the base of the wrist and includes a longitudinal slot in the cannula to allow for a cutting instrument to be inserted into the cannula. The instrument may be advanced through the ligament to divide the ligament, or may be inserted into the distal end of the cannula which protrudes from the palm of the patient so that the cutting instrument may be drawn through the ligament as the cutting instrument extends through the slot in the cannula.
As disclosed in U.S. Pat. Nos. 4,962,770, 4,963,147 and 5,089,000 to Agee et al., an endoscopie instrument for performing carpal tunnel release is provided which includes a pivotable cutting blade which extends outside the sheath to effect cutting of the transverse carpal ligament. An endoscope may be provided for viewing the surgical site. A disadvantage of these instruments is that the blade of the cutting instrument is exposed in such a manner that the control of the instrument to prevent cutting of tissues other than the transverse carpal ligament is minimal, and in effect will allow cutting of any tissue which happens to be in the way of the blade.
Furthermore, these known instruments either require the use of numerous components, such as that disclosed in the Chow patent, or provide instruments with numerous moving parts, such as that disclosed in the Agee et al. patents, which reduce the control of the instrument in the confined area of the carpal tunnel.
Other surgical cutting instruments are known which provide for cutting tissue by pinching the tissue between a cutting blade and a wall or stop member of the instrument. Such an instrument is disclosed in U.S. Pat. No. 5,176,695 to Dulebohn which discloses a hook like cutting member which is dram across a gap in the end of the instrument to hook tissue such as blood vessels. The blood vessels are engaged in the gap against a wall of the instrument to cut the tissue against the wall. Similar instruments are shown in U.S. Pat. No. 3,902,498 to Niederer, U.S. Pat. No. 3,995,619 to Glatzer, and U.S. Pat. No. 4,620,547 to Boebel. A disadvantage of these instruments lies in the fact that they can only cut vessels or other tissues that will fit into the gap so that the tissue may be pinched between the cutting edge and the wall against which the cutting edge is forced.
As disclosed in U.S. Pat. No. 769,829 to Mott, a surgical instrument is provided having a head which houses a rearwardly directed cutting blade which is exposed upon movement of the head away from a housing. As the head is moved away from the housing, an opening or gap is defined between the head and the housing so that the blade may be drawn rearwardly to cut vessels or tissues that are positioned within the gap as the blade moves rearwardly against the housing. This instrument suffers the same disadvantages as the instruments described above which pinch tissue or vessels between the cutting blade and a wall of the instrument
The need exists for a cutting instrument which obviates the disadvantages encountered in the prior art and provides a highly controllable instrument for performing endoscopic surgical procedures such as carpal tunnel release. The instrument should protect the surrounding tissue and ensure that only the tissue intended to be cut, such as the transverse carpal ligament, is cut without damaging surrounding tissue. The instrument should also provide a means for removing the instrument without injuring tissue during its removal. The instrument should advantageously enable the surgical site to be viewed during cutting if used endoscopically.